The U.S. chemical industry generates over a billion tons of hazardous waste each year, corresponding to about 4 tons of hazardous waste per ton of actual product. This waste includes about 600,000 tons of chlorinated waste, which, at present, is disposed of in certified incinerators. These incinerators are expensive to operate and are subject to increasing scrutiny regarding the environmental impact of the effluent gases produced.
There is also a great need for the safe destruction of chemical weapons, both in the U.S. and worldwide. It is estimated that 31,000 tons of mustard gas agents and nerve gas agents are stored around the United States, and plans for incineration of such materials have been met with public opposition.
Halogenated organic compounds, in general, pose a particular environmental threat. Such compounds occur infrequently in nature, and the carbon-halogen bond is generally resistant to natural decomposition methods. Incineration of these compounds is highly regulated and limited in the U.S. The products of such incineration, unless rigorously scrubbed, contribute to acid rain, and include chlorodioxins, which are highly toxic. One class of halocarbons, polyhalogenated biphenyls, are no longer produced in the U.S. and certain other countries, and methods for environmentally sound decomposition of these compounds is the subject of extensive research. Polychlorinated biphenyls (PCB's) and, polybrominated biphenyls (PBB's), long used as flame retardants in plastics and polymers, are highly resistant to decomposition by environmental forces and may enter the food chain with disastrous results.
A number of methods have been used to decompose hazardous or toxic materials such as these to products which are environmentally benign. Such practices include, for example, supercritical water oxidation (SCWO), wet air oxidation, incineration, molten salt oxidation, plasma are disposal, hydrothermal liquid oxidation, and molten metal pyrolysis. Studies of supercritical water oxidation include work by Hossain, Modell, Whitlock, Burleson, Titmas, Jin, Meyer, Ross, and Savage. Most of this work demonstrated a need to overcome slow reaction times, the severe reaction conditions of decomposition of materials, particularly halogenated organic compounds, and the attendant corrosion of the reaction equipment.
Co-owned applications U.S. Ser. No. 08/621,746 and Ser. No. 08/632,604, both allowed, describe a SCWO process which incorporates a heterogeneous reagent, preferably sodium carbonate, in the decomposition chamber. This process provides high reaction rates and conversions and minimizes corrosion of the reaction chambers. In some instances, however, it was found that the solid reagent tended to cake during reaction, thus reducing the reactive surface of the reagent. Thus, methods of maintaining the reagent as a dispersion throughout the reaction have been sought.